Low phase noise MOS LC oscillator

ABSTRACT

A cross-coupled differential MOS oscillator having reduced phase noise is applicable to a RF communication device such as a transmitter or receiver. The oscillator having low phase noise is formed of a frequency dependent amplifier to amplify a signal having a fundamental frequency; a frequency dependent feedback device that is connected between an output of the frequency dependent amplifier and an input of the frequency dependent amplifier to feed a portion of an amplified signal having the fundamental frequency to an input of the frequency dependent amplifier to stimulate oscillation; and a attenuating device in communication with the frequency dependent amplifier. The attenuating device reduces the gain of the frequency dependent amplifier for signals having frequencies much, much less than the fundamental frequency to decrease the phase noise.

This application is based on a provisional patent application,60/204885, filed on May 17, 2000.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to high frequency oscillator circuits. Moreparticularly, this invention relates to metal oxide semiconductors (MOS)oscillators having low phase noise.

2. Description of the Related Art

Inductive/capacitive (LC) oscillators are important elements of anyRadio Frequency (RF) communication devices, such as transmitters, wherethe LC oscillators are used as master oscillators, or as receivers wherethe LC oscillators are used as local oscillators. An importantperformance benchmark of and LC oscillator is the phase noisecharacteristic. An oscillator with a lower phase noise indicates thatthe oscillator produces lower spurious energy outside the desiredfundamental signal tone.

Phase noise is produced as a result of low frequency noise signal foundin active elements used in the oscillator. This low frequency signal ismodulated (up converted) by the fundamental signal tone, resulting inthe spreading of the oscillator frequency energy beyond the intendedtarget frequency. This low frequency noise signal is often referred toas flicker noise (commonly referred to in the literature as 1/f) inbipolar and Metal Oxide Semiconductor (MOS) transistors. The 1/f noiseenergy in bipolar transistors is known to be significantly less thanthat of MOS transistors. This is the reason why practically all lowphase noise LC oscillators are built using bipolar transistors or evenmore esoteric transistors such as Galium-Arsenide devices.

Complementary MOS (CMOS) based LC oscillators are now being investigatedagain for application to systems-on-a-chip (SOC) devices for RFcommunication applications. LC oscillators of the prior art fall farshort of the minimum performance requirements of many of today'swireless communication systems.

A typical example of an LC oscillator in MOS technology is shown in FIG.2. It is based on cross-coupled NMOS transistors M1 and M2, a pair ofinductors L1 and L2, and capacitor C1 and C2 tuning elements. PMOStransistors, which usually have slightly lower 1/f noisecharacteristics, can be used to replace the NMOS transistors M1 and M2at a slight increase in power dissipation and lower maximum operatingfrequency.

A review of a general form of the criteria for designing an oscillatorcircuit of the prior art is shown in FIG. 1. The necessary components ofan oscillator are a frequency dependent gain circuit 100, a frequencydependent feedback circuit 105, and a combining block 110. The output V₀120 of the gain circuit 100 is the input to the feedback circuit 105.The input signal V₁ 115 is combined in the combining block 110 with theoutput V_(fb) 107 of the feedback circuit 105 to form the input 112 ofthe gain circuit 100.

The gain of the gain block 100 is designated (G(jω) and the gain of thefeedback circuit 105 is designated H(jω). These gains G(jω) and H(jω)describe the relationship of their respective output signals V_(o) 120and V_(fb) 107 to their respective input signals 112 and V_(o) 120.Therefore, the output signal V_(o) 120 becomes$V_{o} = \frac{V_{i}{G\left( {j\quad \omega} \right)}}{1 + {{G\left( {j\quad \omega} \right)}{H\left( {j\quad \omega} \right)}}}$

For an oscillator, the output signal V_(o) 120 must be nonzero even ifthe input voltage V₁ 115 is zero. For this to be true, then

1+G(jω)H(jω)=0

or

G(jω)H(jω)=−1

That is, the magnitude of the open-loop transfer function must be equalto 1 and the phase shift of the gain circuit 100 and the feedbackcircuit 105 must be 180°.

In FIG. 2, the gain circuit of the oscillator is formed by thedifferentially cross-connected pair of transistors M1 and M2 and theconstant current source I1. The frequency dependent gain determiningimpedances are formed by the inductors L1 and L2 and the capacitors C1and C2.

The feedback circuit is accomplished by the connecting of the drain ofthe NMOS transistor M1 to the gate of the NMOS transistor M2 and thedrain of the NMOS transistor M2 to the gate of the NMOS transistor M1.This forms a cross-coupled differential oscillator.

A CMOS oscillator of the prior art is illustrated in FIG. 3. In thiscase, the gain circuit is formed by the differentially connected pair ofNMOS transistors M1 and M2, the differentially connected pair of PMOStransistors M3 and M4, and the current sources I1 and I2. As describedabove, the frequency dependent gain determining impedances are formed bythe inductors L1 and L2 and capacitors C1 and C2.

The fundamental frequency f0 of a cross coupled differential oscillatoris determined by the formula:$\omega = {{\frac{1}{\sqrt{L_{eff}C_{eff}}}\quad {such}\quad {that}\quad f_{o}} = \frac{1}{2\pi \sqrt{L_{eff}C_{eff}}}}$

where:

L_(elf) is the value of the effective inductance of the inductors L1 andL2.

C_(eff) is the value of the effective capacitance of the capacitors C1and C2.

For the structure of the design where the inductors are mutually coupledthen the effective inductance is:

L _(eff)=4L 1=4L 2

The effective capacitance of the capacitors C1 and C2 is the parallelcombination of the two capacitors C1 and C2 and is:

C _(eff)=½C 1=½C 2

Combining the above, the frequency of the oscillators of FIGS. 2 and 3is: $f_{o} = {\frac{1}{2\pi \sqrt{2{L1C2}}}.}$

It should be noted that the capacitances C1 and C2 included theparasitic capacitances of the oscillator circuit.

It is well known in the art that phase noise is the result of smallperturbations in phase due to small random shifts in oscillatorfrequency. These shifts are caused by thermal noise, shot noise, andflicker noise (1/f noise). These noises are functions of the devicecharacteristics of the NMOS transistors M1 and M2 of FIGS. 2 and 3 andthe PMOS transistors M3 and M4 of FIG. 3. The phase noise is modeled assmall voltage sources Vn1 and Vn2 at the gates of the NMOS transistorsM1 and M2 of FIGS. 2 and 3 and voltage sources Vp1 and Vp2 at the gatesof the PMOS transistors M4 and M4 of FIG. 3.

The flicker noise (1f/noise) is a function of the active devicecharacteristics of the NMOS transistors M1 and M2 of FIGS. 1 and 2 andPMOS transistors M3 and M4 of FIG. 3.

The advancements in scaling of the device features in semiconductorprocessing allow multi-gigahertz operating frequencies to be readilyachievable. Unfortunately, the same scaling down of MOS transistors havethe opposite effect on the 1/f noise characteristics. The smaller devicegeometries are, the higher the 1/f noise components, leading to higherphase noise on the final oscillator.

“A 1.8 Ghz CMOS Voltage-Controlled Oscillator”,—Razavi, B., Digest ofTechnical Papers, 43rd ISSCC, 1997, pp. 388-389 and shown in FIG. 4describes a structure of having multiple oscillators OSC1 and OSC2coupled together to oscillate in quadrature or 90° out-of-phase. Theoscillator OSC1 and OSC2 are structured and function as described inFIG. 2. The differential pair of NMOS transistors M3 and M4 and thecurrent source 12 form a first coupling circuit. The first couplingcircuit has an in-phase input that is formed by the gate of the NMOStransistors M3 and a out-of-phase input that is formed by the gate ofthe NMOS transistors M4. The first coupling circuit has a in-phaseoutput that is formed by the drain of the NMOS transistor M4 and anout-of-phase output that is formed by the drain of the NMOS transistorM3. The in-phase input of the first coupling circuit is connected to thedrain of the NMOS transistor M5 and the gate of the NMOS transistor M6.The out-of-phase input of the first coupling circuit is connected to thedrain of the NMOS transistor M6 and the gate of the NMOS transistor M5.The in-phase output of the first coupling circuit is connected to thedrain of the NMOS transistor M2 and the gate of the NMOS transistor M1.The out-of-phase output of the first coupling circuit is connected tothe drain of the NMOS transistor M1 and the gate of the NMOS transistorM2.

The differential pair of NMOS transistors M7 and M8 and the currentsource 14 form a second coupling circuit. The second coupling circuithas an in-phase input that is formed by the gate of the NMOS transistorsM7 and a out-of-phase input that is formed by the gate of the NMOStransistor M8. The second coupling circuit has a in-phase output that isformed by the drain of the NMOS transistor M8 and an out-of-phase outputthat is formed by the drain of the NMOS transistor M7. The in-phaseinput of the second coupling circuit is connected to the drain of theNMOS transistor M2 and the gate of the NMOS transistor M1. Theout-of-phase input of the second coupling circuit is connected to thedrain of the NMOS transistor M1 and the gate of the NMOS transistor M2.The in-phase output of the second coupling circuit is connected to thedrain of the NMOS transistor M6 and the gate of the NMOS transistor M5.The out-of-phase output of the second coupling circuit is connected tothe drain of the NMOS transistor M6 and the gate of the NMOS transistorM5.

The structure as shown generates two oscillatory signals, one betweenthe drains of the NMOS transistors M1 and M2 and one between the drainsof the NMOS transistors M5 and M6. The two oscillatory signals are inquadrature or 90° out of phase. The quadrature oscillator as describedis subject to the phase noise problems as above-described.

“Design Issues in CMOS Differential LC Oscillators,” Hajimiri, A., Lee,T. H., IEEE Journal of Solid-State Circuits, pp. 717-724, May 1999 Vol.34 Issue No. 5, presents an analysis of phase noise in differentialcross-coupled inductance-capacitance (LC) oscillators. The effect oftail current and tank powder dissipation on the voltage amplitude isshown. Various noise sources in the complementary cross-coupled pair areidentified, and their effect on phase noise is analyzed.

“Phase Noise in CMOS Differential LC Oscillators”, Hajimiri, A., Lee, T.H., Digest of Technical Papers—1988 Symposium on VLSI Circuits, 1988,pp. 48-51, describes an analysis of phase noise in differentialcross-coupled tuned tank voltage controlled oscillators. The effect ofactive device noise sources as well as the noise due to the passiveelements is taken into account.

U.S. Pat. No. 5,475,345 (Gabara) teaches a CMOS coupled-tank oscillatorhaving two inverters coupled, input-to-output, by inductances that maybe simply wires, and a capacitance acting in parallel with each inverterthat may be, simply, the inverter's gate capacitance.

U.S. Pat. No. 5,850,163 (Drost, et al.) discusses an active inductoroscillator with wide frequency range. The active inductor oscillatorincludes a tank circuit, buffer and integrating circuit that usedifferential transistor pairs that reduce phase jitter due to externalcommon-mode noise sources.

U.S. Pat. No. 5,959,504 (Wang) describes a voltage controlled oscillatorCMOS circuit using back gate terminals of CMOS transistors to vary theparasitic capacitances of the transistors. The back gate terminalsreceive a signal from a variable voltage source so that oscillation canbe controlled by adjusting the variable voltage.

“A Low-Noise, 900-MHz VCO in 0.6um CMOS” (Park, et al), IEEE Journal OfSolid-State Circuits, Vol. 34, pp 586-591, May 1999, Issue No. 5,describes a low-noise, 900 MHz, voltage controlled oscillator (VCO)fabricated in a 0.6-um CMOS technology. The VCO consists of four-stagefully differential delay cells performing full switching. It utilizesdual-delay path techniques to achieve high oscillation frequency andobtain a wide tuning range.

“10 MHz CMOS OTA-C Voltage-Controlled Quadrature Oscillator,”Linares-Barranco, et al., IEEE Electronics Letters, June 1989, pp.765-767, Vol. 25, Issue No. 12, details a quadrature-typevoltage-controlled oscillator with operational transconductanceamplifiers and capacitors (OTA-C).

“RC Sequence Asymmetric Polyphase Networks for RF IntegratedTransceives,” Galal et al. Transactions On Circuits And Systems—II:Analog And Digital Signal Processing, January 2000, pp. VOL 47, IssueNo. 1, describes Resistance-Capacitance (RC) sequence asymmetricpolyphase networks. A sequence of asymmetric polyphase networks providethe generation of highly matched wide-band quadrature signals which areimmune to components mismatch, and suppression of the image signalswithout the need for highly selective RF filters and without employingimage-reject mixing technique.

U.S. Pat. No. 5,714,911 (Gilbert) describes a quadrature oscillator thatincludes an amplitude control circuit. The amplitude control circuit isthat is based upon the trigonometric identity sin²(Ωt)+cos²(Ωt)=1. Theamplitude control circuit, referred to as a Pythagorator, includes twosquaring circuits. Each squaring circuit receives a respectivequadrature oscillator signal and squares it. The outputs of the twosquaring circuits are joined together so as to sum the outputs of thetwo squaring circuits to produce a sum of squares signal. This signal, acurrent in the preferred embodiment, is provided to damping diodescoupled to the outputs of the quadrature oscillator. The damping diodesproduce a shunt positive resistance at the outputs of the quadratureoscillator in response to this current that has the effect of cancelingthe shunt negative resistance of the regenerative elements of theoscillator thereby establishing the amplitude of the quadratureoscillator signals at a desired amplitude.

U.S. Pat. No. 5,949,295 (Schmidt) teaches an integratable tunableresonant circuit for use in filters and oscillators. The circuitincorporates differential amplifier stage with a pair of differentiallyconnected transistors with two negative feedback resistors. The twonegative feedback resistors increase the linearity range of an inputvoltage of the differential amplifier stage.

U.S. Pat. No. 6,008,701 (Gilbert) details a quadrature oscillator usinginherent nonlinearities of impedance cells to limit amplitude. Thequadrature oscillator based on two cross-coupled integrator cellsutilizing the inherent nonlinearity of positive and negative impedancecells to control the amplitude of oscillation. The oscillator issimplified thus eliminating the need for an outer control loop. Anegative impedance cell is coupled to each integrator cell for assuringproper start-up and enhancing the amplitude of oscillation. A positiveimpedance cell is also coupled to each integrator cell to dampen theamplitude of oscillation. The transconductance of each impedance cellvaries in response to the bias current provided to the cell. Thus, bycontrolling the bias currents through the cells, the negative andpositive impedances seen by each integrator cell can made to cancel atthe desired oscillation amplitude, so that the circuit oscillateswithout any damping or enhancement. By utilizing the inherentnonlinearity of positive and negative impedance cells, the bias currentsprovided to the impedance cells can remain fixed for a given frequencyof operation, thereby simplifying the design of the oscillator andproviding precise, robust control.

SUMMARY OF THE INVENTION

An object of this invention is to provide a cross-coupled differentialMOS oscillator.

Another object of this invention is to provide a cross-coupleddifferential MOS oscillator having reduced phase noise.

Another object of this invention is to provide a RF communicationdevice, e.g., a transmitter or receiver, having a cross-coupleddifferential MOS oscillator.

To accomplish these and other objects, an oscillator having low phasenoise that is formed of a frequency dependent amplifier to amplify asignal having a fundamental frequency; a frequency dependent feedbackdevice that is connected between an output of the frequency dependentamplifier and an input of the frequency dependent amplifier to feed aportion of an amplified signal having the fundamental frequency to aninput of the frequency dependent amplifier to stimulate oscillation; anda attenuating device in communication with the frequency dependentamplifier. The attenuating device reduces the gain of the frequencydependent amplifier for signals having frequencies much, much less thanthe fundamental frequency to decrease the phase noise.

The frequency dependent amplifier has an amplifying means. Theamplifying means has an input and an output, whereby a signal at theinput is amplified by a gain factor to form a signal at the output. Thefrequency dependent amplifier further, has a frequency dependent gaindetermining in communication with the amplifying means. The frequencydependent gain determining impedance determines the frequency at whichthe maximum gain of the frequency dependent amplifier occurs.

The amplifying means is composed of a pair of cross-coupled MOStransistors. The drain of each MOS transistor is connected to a gate ofthe other MOS transistor and to a port of the frequency dependent gaindetermining impedance. A first current source is connected to a sourceof one of the MOS transistors and to a ground reference point and to afirst port of the attenuating device. A second current source isconnected to a source of the other MOS transistor and to a second portof the attenuating device.

The frequency dependent determining impedance is formed by at least oneinductor in communication with the amplifying means and a power supplyvoltage source, and at least one capacitor in communication with theamplifying means and a ground reference point.

The attenuating device is in the preferred embodiment, a capacitor incommunication with the sources of the cross-coupled MOS transistors. Thevalue of the capacitor is selected such that the fundamental frequencyof oscillation is from approximately 10 times to approximately 20 timesthe high pass bandwidth of the cross-coupled MOS transistors.

Alternately, the amplifying means is formed of a cross-coupled pair ofMOS transistors of the first conductivity type and a cross-coupled pairof MOS transistors of the second conductivity type to form a CMOSamplifying means. The drain of each MOS transistor of the firstconductivity type is connected to a gate of the other MOS transistor ofthe first conductivity type and to a port of the frequency dependentgain determining impedance. A first current source is connected to asource of one of the MOS transistors of the first conductivity type andto a first port of the attenuating device, and a second current sourceis connected to a source of the other MOS transistor of the firstconductivity type and to a second port of the attenuating device.

The drain of each MOS transistor of the second conductivity type isconnected to a gate of the other MOS transistor of the secondconductivity type and to one port of the frequency dependent gaindetermining impedance. A third current source in communication with asource of one of the MOS transistors of the second conductivity type andto a third port of the attenuating device, and a fourth current sourcein communication with a source of the other MOS transistor of the secondconductivity type and to a fourth port of the attenuating device.

The attenuating device in the CMOS embodiment of the amplifying means iscomposed of a first capacitor connected from the first port to thesecond port of the gain attenuating means and a second capacitor incommunication with the third and fourth ports of the gain attenuatingmeans.

An application of the cross-coupled differential MOS oscillator is asthe carrier oscillator of an RF transmitter. Alternately, thecross-coupled differential MOS oscillator is the local oscillator of anRF receiver that is used to demodulate the incoming RF signal.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a system block diagram of a frequency dependent system withfeedback of the prior art.

FIG. 2 is a schematic diagram of a cross-coupled differential NMOSoscillator of the prior art.

FIG. 3 is a schematic diagram of a cross-coupled differential CMOSoscillator of the prior art.

FIG. 4 is a schematic diagram of a quadrature oscillator of the priorart.

FIGS. 5a and 5 b are schematic diagrams of two embodiments ofcross-coupled differential MOS oscillators of this invention.

FIGS. 6a and 6 b are schematic diagrams of the cross-coupleddifferential MOS oscillator of this invention (FIG. 5a) operating at lowfrequencies (FIG. 6a) and at high frequencies (FIG. 6b).

FIG. 7 is a schematic diagram of a cross-coupled differential CMOSoscillator of this invention.

FIG. 8 is a schematic diagram of a quadrature oscillator having lowphase noise of this invention having.

FIG. 9 is a block diagram of a multiple frequency transforming circuithaving low phase noise of this invention.

FIG. 10 is a schematic diagram of a differential amplifier having lowphase noise of this invention.

FIG. 11 is a plot of the spectral display of the phase noise versus thefrequency offset from the fundamental frequency.

FIG. 12a is a schematic diagram of an ideal current source implementedby a biased MOSFET.

FIG. 12b is a schematic diagram of a current source of FIG. 12a havingthe noise component represented as a voltage source.

FIG. 12c is a schematic diagram of a current source of FIG. 12a havingthe noise component represented as a parallel current source.

FIG. 13a is a current source implemented as a programmable resistance.

FIG. 13b is an example of a programmable resistance of FIG. 13a.

FIG. 14a is a current source implemented as an inductance andprogrammable resistance.

FIG. 14b is an example of a programmable resistance of FIG. 14a.

FIG. 14c is an example of programmable inductance/resistance of FIG.14a.

DETAILED DESCRIPTION OF THE INVENTION

Refer now to FIG. 5a for a discussion of the cross-coupled differentialNMOS oscillator having low phase noise of this invention. The frequencydependent gain amplifier is formed by the NMOS transistors M1 and M2 andthe constant current sources I1 and I2. The frequency dependent gaindetermining impedance is formed by the inductors L1 and L2 and thecapacitors C1 and C2.

The inductor L1 is connected from the drain of the NMOS transistors M1to the reference voltage source V_(cc) and the inductor L2 is connectedfrom the drain of the NMOS transistor M2 to the reference voltage sourceV_(cc). The capacitor C1 is connected from the drain of NMOS transistorM1 to the ground reference point and the capacitor C2 is connected fromthe drain of the NMOS transistor M2 to the ground reference point. It isapparent to those skilled in the art that, while the capacitors C1 andC2 are connected to the ground reference point, the capacitors C1 and C2may be connected to any reference voltage source or to any power supplyvoltage source and not effect the operation of the oscillator asexplained above.

The fundamental frequency f₀ of the cross-coupled differentialoscillator of this invention is determined as:$\omega = \frac{1}{\sqrt{2L_{1}C_{1}}}$

such that $f_{o} = \frac{1}{2\pi \sqrt{2L_{1}C_{1}}}$

where:

L₁ is the value of the inductance of the inductor L1 or L2.

C₁ is the value of the capacitance of the

capacitor C1 or C2.

The drain of the NMOS transistor M1 is connected to the gate of the NMOStransistor M2 and the drain of the NMOS transistor M2 is connected tothe gate of the NMOS transistor M1. This cross-coupling of the drains tothe gates of the NMOS transistors M1 and M2 forms the feedback circuitof the oscillator.

The source of the NMOS transistor M1 is connected to the constantcurrent source I1 and the source of the NMOS transistor M2 is connectedto the constant current source I2. The decoupling capacitor C_(c) isconnected between the sources of the NMOS transistors M1 and M2 to actas a gain-attenuating device.

Refer now to FIGS. 6a and 6 b to understand the operation of thecross-coupled differential oscillator of this invention. The decouplingcapacitor C_(c) is chosen to have very high impedance at frequenciesmuch, much lower than the fundamental frequency f₀ of the cross-coupleddifferential NMOS oscillator of FIG. 6a. At frequencies much lower thanthe fundamental frequency f₀, the cross-coupled differential NMOSoscillator of this invention functions as shown in FIG. 6a. The currentsources are separated and the gain of the frequency dependent gaincircuit formed by the NMOS transistors M1 and M2 and the current sourcesI1 and I2 becomes much, much less than one, preventing the flicker noiseor 1/f noise of the noise voltage sources Vn1 and Vn2 from beingamplified and being added to the output signal of the cross-coupleddifferential NMOS oscillator of this invention.

At the fundamental frequency f₀, the decoupling capacitor C_(c) ischosen to have an impedance that is very low. Thus, the cross-coupleddifferential NMOS oscillator of this invention functions as shown inFIG. 6b. The frequency dependent gain circuit formed by the NMOStransistors M1 and M2 and the constant current sources I1 and I2function as described in FIG. 2. The constant current sources I1 and I2are summed together to form effectively one current source (I1+I2).Thus, the frequencies at the fundamental frequency f₀ are amplified. Thefrequency gain determining impedance formed by the inductors L1 and L2and the capacitors C1 and C2 insure that the peak gain of the frequencydependent gain circuit is at the fundamental frequency f₀ and that thehigher and lower frequencies are attenuated.

The noise voltage sources Vn1 and Vn2 are, as described above, themodels of the flicker or 1/f noise that is caused by the devicecharacteristics of the NMOS transistors M1 and M2. The noise voltagesources Vn1 and Vn2 having frequency content that is much less than thefundamental frequency f₀ and thus will be attenuated as shown in FIG.6a.

The high pass bandwidth (BW) of the cross-coupled differentialoscillator is a function of the transconductance of the NMOS M1 and M2and the value of the decoupling capacitor Cc and is determined by theformula: ${BW} = {\frac{g_{m}}{2\pi \quad {Cc}}.}$

The high pass bandwidth BW must be maintained at a level that is much,much smaller than the cutoff frequency of the cross-coupled differentialoscillator to prevent loss of the fundamental frequency signal. Thedecoupling capacitor Cc should be chosen such that the fundamentalfrequency f0 of the cross-coupled differential oscillator is fromapproximately ten times to approximately twenty times the high passbandwidth BW of the cross-coupled oscillator.

FIG. 5b illustrates a second embodiment of a cross-coupled differentialNMOS oscillator of this invention. The frequency dependent gainamplifier in this case is formed by the NMOS transistors M1 and M2 andthe resistors R1 and R2. The resistor R1 is connected between the sourceof the NMOS transistor M1 and the ground reference point. The resistorR2 is connected between the source of the NMOS transistor M2 and theground reference point.

The inductor L1 is connected from the drain the NMOS transistor M1 tothe reference voltage source V_(cc) and the inductor L2 is connectedfrom the drain of the NMOS transistor M2 to the reference voltage sourceV_(cc). The capacitor C1 is connected from the drain of NMOS transistorM1 to the ground reference point and the capacitor C2 is connected fromthe drain of the NMOS transistor M2 to the ground reference point. Asdescribed above, it is apparent to those skilled in the art that, whilethe capacitors C1 and C2 are connected to the ground reference point,the capacitors C1 and C2 may be connected to any reference voltagesource or to any power supply voltage source and not effect theoperation of the oscillator.

The decoupling capacitor Cc2 is connected between the sources of theNMOS transistors M1 and M2 and acts as gain attenuating device asabove-described.

A third embodiment of this invention, as shown in FIG. 7, implements thefrequency dependent gain circuit as a cross-coupled differential CMOSamplifier. The frequency dependent gain circuit is formed by the NMOStransistors M1 and M2, the P-type MOS (PMOS) transistors M3 and M4, andthe current sources I1, I2, I3, and I4.

The drain of the NMOS transistors M1 is connected to the gate of theNMOS transistor M2 and the drain of the NMOS transistor M2 is connectedto the gate of the NMOS transistor M1. Similarly, the drain of the PMOStransistor M3 is connected to the gate of the PMOS transistor M4 and thedrain of the PMOS transistor M4 is connected to the gate of the PMOStransistor M3. The cross-coupling of the drains and gates of the NMOStransistors M1 and M2 and the PMOS transistors M3 and M4 forms thefeedback circuit of the oscillator.

The inductor L1 is connected between the drains of the NMOS and PMOStransistors M1 and M3 and the reference voltage source V_(cT). Theinductor L2 is connected between the drains of the NMOS and PMOStransistors M2 and M4 and the reference voltage source V_(cT). Thecapacitor C1 is connected between the drains of the NMOS and PMOStransistors M1 and M3 and the ground reference point. The capacitor C2is connected between the drains of the NMOS and PMOS transistors M2 andM4 and the ground reference point. Again, as described above, it isapparent to those skilled in the art that, while the capacitors C1 andC2 are connected to the ground reference point, the capacitors C1 and C2may be connected to any reference voltage source or to any power supplyvoltage source and not effect the operation of the oscillator.

The inductors L1 and L2 and the capacitors C2 and C2 form the frequencydependent gain determining impedance.

The constant current source I1 is connected to the source of the NMOStransistors M1, and the constant current source I2 is connected to thesource of the NMOS transistors M2. Similarly, the constant currentsource I3 is connected to the source of the PMOS transistor M3 and theconstant current source I4 is connected to the source of the PMOStransistor M4.

The gain-attenuating circuit is formed by the decoupling capacitorsC_(c) 3 and C_(c) 4. The decoupling capacitor C_(c) 3 is connectedbetween the sources of the NMOS transistors M1 and M2. The decouplingcapacitor C_(c) 4 is connected between the sources of the PMOStransistors M3 and M4.

The gain-attenuating circuit (C_(c) 3 and C_(c) 4) functions much asdescribed in FIGS. 6a and 6 b. For frequencies much, much less than thefundamental frequency f₀, the decoupling capacitors C_(c) 3 and C_(c) 4have a large impedance and force the gain of the frequency dependentgain circuit to a level much, much less than one to attenuate the lowfrequency flicker or 1/f noise. Conversely, for frequencies equal to thefundamental frequency f_(c), the decoupling capacitors Cc3 and Cc4 havelow impedance and the frequency dependent gain circuit functionsequivalently to that described in FIG. 3. The constant current sourcesI1 and I2 are summed as described in FIG. 5b and, similarly, theconstant current sources I3 and I4 are summed together to functionequivalently to the description of FIG. 3.

The high pass bandwidth (BW) of the cross-coupled differentialoscillator is a function of the transconductance of the NMOS M1 and M2and the value of the decoupling capacitor Cc3 and the transconductanceof the PMOS transistors M3′ and M4 and the value of the decouplingcapacitor Cc4 and is determined by the formula:${BW} = {\frac{g_{m}}{2\pi \quad {Cc}}.}$

The high pass bandwidth BW must be maintained, as described above, at alevel that is much, much smaller than the cutoff frequency of thecross-coupled differential oscillator to prevent loss of the fundamentalfrequency signal f₀. The decoupling capacitor Cc should be chosen suchthat the fundamental frequency f₀ of the cross-coupled differentialoscillator is from approximately ten times to approximately twenty timesthe high pass bandwidth BW of the cross-coupled oscillator.

FIG. 8 illustrates a quadrature oscillator having low phase noise ofthis invention. The cross-coupled differential oscillators OSC1 and OSC2are structured and function as cross-coupled differential oscillators asdescribed in FIG. 5a. The NMOS transistors M3 and M4 and the currentsources I3 and I4 form a first coupling circuit. The current source I3is connected between the source of the NMOS transistor M3 and the groundreference point. The current source I4 is connected between the sourceof the NMOS transistor M4 and the ground reference point. The gate ofthe NMOS transistor M3 functions as the in-phase input of the firstcoupling circuit and the gate of the NMOS transistor M4 functions as theout-of-phase input of the first coupling circuit. The drain of the NMOStransistor M4 functions as the in-phase output of the first couplingcircuit and the drain of the NMOS transistor M3 functions as theout-of-phase output of the first coupling circuit. The decouplingcapacitor Cc6 is connected between the sources of the NMOS transistorsM3 and M4. The decoupling capacitor Cc6 is chosen to function similar tothe decoupling capacitor Cc of FIG. 5a to eliminate the phase noise fromthe first coupling circuit.

The in-phase input of the first coupling circuit is connected to thedrain of the NMOS transistor M5 and the gate of the NMOS transistor M6of the second cross-coupled differential oscillator OSC2. Theout-of-phase input of the first coupling circuit is connected to thedrain of the NMOS transistor M6 and the gate of the NMOS transistor M5of the second cross-coupled differential oscillator OSC2. The in-phaseoutput of the first coupling circuit is connected to the drain of theNMOS transistor M2 and the gate of the NMOS transistor M1 of the firstcross-coupled differential oscillator OSC1. The out-of-phase output ofthe first coupling circuit is connected to the drain of the NMOStransistor M1 and the gate of the NMOS transistor M2 of the firstcross-coupled differential oscillator OSC1.

The NMOS transistors M7 and M8 and the current sources I7 and I8 formthe second coupling circuit. The current source I7 is connected betweenthe source of the NMOS transistor M7 and the ground reference point. Thecurrent source I8 is connected between the source of the NMOS transistorM8 and the ground reference point. The gate of the NMOS transistor M7functions as the in-phase input of the second coupling circuit and thegate of the NMOS transistor M4 functions as the out-of-phase input ofthe second coupling circuit. The drain of the NMOS transistor M7functions as the in-phase output of the second coupling circuit and thedrain of the NMOS transistor M8 functions as the out-of-phase output ofthe second coupling circuit. The decoupling capacitor Cc8 is connectedbetween the source of the NMOS transistors M7 and M8. The decouplingcapacitor Cc8 is chosen to function similar to the decoupling capacitorCc of FIG. 5a to eliminate the phase noise from the first couplingcircuit.

The in-phase input of the second coupling circuit is connected to thedrain of the NMOS transistor M1 and the gate of the NMOS transistor M2of the first cross-coupled differential oscillator OSC1. Theout-of-phase input of the second coupling circuit is connected to thedrain of the NMOS transistor M2 and the gate of the NMOS transistor M1of the first cross-coupled differential oscillator OSC1. The in-phaseoutput of the second coupling circuit is connected to the drain of theNMOS transistor M6 and the gate of the NMOS transistor M5 of the secondcross-coupled differential oscillator OSC2. The out-of-phase output ofthe second coupling circuit is connected to the drain of the NMOStransistor M5 and the gate of the NMOS transistor M6 of the secondcross-coupled differential oscillator OSC2.

The in-phase and the out-of-phase of the first coupling circuit aretransposed relative to the similar in-phase and out-of-phase connectionsof the second coupling circuit. This transposition is to force thenecessary phase shift to cause the cross-coupled differentialoscillations OSC1 and OSC2 to oscillate in quadrature or 90° out ofphase as described above in Razavi.

The structure of the oscillator of FIG. 8 is generalized to a structureas shown in FIG. 9. This circuit is used to create multiple phasedoscillators, mixers, modulators, demodulators, and any circuit requiringthe transforming of the an input signal with multiple frequencies. Thefrequency transforming circuit of FIG. 9 has multiple coupling elementsCE1, CE2, . . . , CEn that are serially connected output to input. Thefrequency transforming circuit, further, has multiple cross-coupleddifferential oscillators OSC1, OSC2, . . . , OSCn. The output of each ofthe multiple cross-coupled differential oscillators OSC1, OSC2, . . . ,OSCn is connected to an input of one of the coupling elements couplingelements CE1, CE2, . . . , CEn.

The input signal is developed between the input terminals IN+ and IN−and is transferred to the first coupling element CE1. The input signalis then combined with the oscillatory signal from the firstcross-coupled differential oscillator OSC1. The signal at the output ofthe first coupling element CE1 is transferred to the input the secondcoupling element CE2 where it is combined with the second oscillatorysignal from the second cross-coupled differential oscillator OSC2. Thesignal at the output of the second coupling element CE2 is transferredto the following coupling elements CEn for combination with theoscillatory signals from the subsequent oscillators OSCn. The signalfrom the final coupling element CEn is transferred to subsequentcircuitry. In the alternative, the output of the last coupling elementCEn may be connected to the input of the first coupling element CE1 tofeedback the output signal (or a portion of the output signal) to theinput of the circuit.

The coupling elements coupling elements CE1, CE2, . . . , CEn, inaddition to combining the oscillatory signals from the multiplecross-coupled differential oscillators OSC1, OSC2, . . . , OSCn, mayprovide phase shifting for a multiple phased oscillator, or anyappropriate filtering, integrating, differentiating function.

Further, the outputs of each of the coupling elements CE1, CE2, . . . ,CEn is connected to an input of a buffering amplifier BUF1, BUF2, . . .. , BUFn. Each of the a buffering amplifiers BUF1, BUF2, . . . , BUFncapture the output of one of the coupling elements CE1, CE2, . . . , CEnand amplifies and isolates the signal to form the output signals φ1, φ2,. . . , φn that are transferred to external circuitry.

Each cross-coupled differential oscillators OSC1, OSC2, . . . , OSCn,each coupling element CE1, CE2, . . . , CEn, and each bufferingamplifier BUF1, BUF2, . . . , BUFn has a differential amplifier with lowphase noise of this invention as shown in FIG. 10. The differentialamplifier is formed by the NMOS transistors M1 and M2 and the currentsources I1 and I2.

The gates of the NMOS transistors M1 and M2 respectively form thein-phase input IN+ and the out-of-phase input IN−. The drains of theNMOS transistors M1 and M2 respectively form the in-phase output OUT+and the out-of-phase output OUT−.

The current source I1 is connected between the source of the NMOStransistor M1 and the ground reference point. The current source I2 isconnected between the source of the NMOS transistor M2 and the groundreference point.

The decoupling capacitor Cc is connected between the sources of the NMOStransistors M1 and M2 to provide the necessary gain attenuating toeliminate the phase noise. When the differential amplifier is operatingat sufficiently high frequency, the impedance of the decouplingcapacitor Cc is very low and the current sources I1 and I2 combine. Thedifferential amplifier operates as a true differential amplifier havingvery high gain. However, if the frequency of operation is sufficientlylow, the impedance of the decoupling capacitor Cc is very high and thegain of the differential amplifier is very low, thus attenuating thesignals of the phase noise.

The high pass bandwidth BW of the differential amplifier of thisinvention is a function of the transconductance (g_(m)) of the NMOStransistors “looking” into the sources and is determined by the formula:${BW} = {\frac{g_{m}}{2\pi \quad {Cc}}.}$

For the most successful operation of the differential amplifier thedecoupling capacitor Cc should be chosen such that the fundamentalfrequency f0 of the cross-coupled differential oscillator is fromapproximately ten times to approximately twenty times the high passbandwidth BW of the cross-coupled oscillator. This insures that thefundamental frequency f0 is not affected by the operation of thedecoupling capacitor Cc.

FIG. 11 is plots 700 and 750 that illustrate the spectral density of thephase noise of the output signal versus the frequency offset from thefundamental frequency f₀ of cross-coupled differential oscillators ofthis invention 700 and the prior art. As can be seen, the spectraldensity of the phase noise of the cross-coupled differential NMOStransistor is lower than an equivalent design of the prior art.

FIG. 12a is an example of an ideal current source utilized by thepresent invention. In FIG. 12a the ideal current source is implementedas a MOS transistor which is biased so that the MOS transistor operatesin the saturation region. Such a current source may generate a 1/f noisecomponent, which can be significant in MOS devices. This problem isexacerbated at higher frequencies, in which the oscillator of thepresent invention is designed to operate. Additionally, as the devicegeometry becomes small the 1/f noise becomes more pronounced. FIG. 12cillustrates an equivalent representation showing a current source I anda noise component current source I_(noise).

A conventional solution to reduce or eliminate the 1/f noise is toutilize a resistor as the current source. However, it is difficult toset the appropriate amount of resistance for the oscillator to functionproperly. In accordance with an embodiment of the present invention aprogrammable resistance R is utilized as the current source, as shown inFIG. 13a. The programmable resistance can insure the appropriate amountof resistance to provide the current to the oscillator. The programmableresistance may be implemented as a switched resistor array. One exampleof the resistor array is shown in FIG. 13b. The resistor array showntherein comprises resistors R1-Rn and associated switches S1-Sn. Ofcourse as will be appreciated by one of ordinary skill in the art, otherresistor configurations may be employed and are within the scope andspirit of the present invention.

An alternative embodiment of the current source in accordance with thepresent invention is to utilize an inductance L in series with aprogrammable resistance R, as shown in FIG. 14a. As with the previousembodiment there is no 1/f noise, since the inductance and resistanceare passive components. This configuration behaves like a constantcurrent source regardless of the input voltage, especially if theinductance is sufficiently high, at high frequencies the current isessentially constant (due to the inductance properties). In thisembodiment of the programmable resistance may be implemented as aswitched resistor array. One example shown therein comprises resistorsR1-Rn and associated switches S1-Sn. Of course as will be appreciated byone of ordinary skill in the art, other resistor configurations may beemployed and are within the scope and spirit of the present invention.The inductance L inherently has some resistance. Accordingly, theinductance and programmable resistance may be alternatively be implementby a switched inductance array, wherein each inductance inherently hasthe appropriate amount of resistance.

It will be apparent to those skilled in the art that the NMOStransistors M1 and M2 of FIG. 5a can be replaced by PMOS transistorswith appropriate changes to the power supply voltage source V_(cc) andthe ground reference point. Further, it would be apparent that the NMOStransistors could be replaced by bipolar junction transistors or otherfield effect transistors constructed of materials such asGalium-Arsenide and still be in keeping with this invention.

While this invention has been particularly shown and described withreference to the preferred embodiments thereof, it will be understood bythose skilled in the art that various changes in form and details may bemade without departing from the spirit and scope of the invention.

The invention claimed is:
 1. An oscillator having a fundamentalfrequency and having low phase noise comprising: a frequency dependentamplifier; a frequency dependent feedback device in communication withan output of said frequency dependent amplifier and an input of saidfrequency dependent amplifier; and an attenuating device incommunication with said frequency dependent amplifier to attenuateflicker noise, wherein said attenuating device has a characteristic suchthat the fundamental frequency is from approximately ten times to twentytimes a high pass bandwidth of a combination of the frequency dependentamplifier and the attenuating device, wherein said frequency dependentamplifier comprises another attenuating device.
 2. The oscillator ofclaim 1 wherein said frequency dependent amplifier amplifies an input bya predetermined gain factor, and wherein said frequency dependentfeedback device comprises: a frequency dependent gain determiningimpedance in communication with said amplifier, wherein a maximum gainof said frequency dependent amplifier occurs at the fundamentalfrequency.
 3. The oscillator of claim 2 wherein said amplifiercomprises: a pair of cross-coupled MOS transistors having a drain ofeach of said pair of cross-coupled MOS transistors being incommunication with a gate of the other of said pair of cross-coupled MOStransistors and to a corresponding terminal of said frequency dependentgain determining impedance; a first current source having a firstterminal in communication with a source of a first one of said pair ofcross-coupled MOS transistors and to a first terminal of saidattenuating device; and a second current source having a first terminalin communication with a source of a second one of said pair ofcross-coupled MOS transistors and to a second terminal of saidattenuating device.
 4. The oscillator of claim 2 wherein said frequencydependent gain determining impedance comprises: at least one inductor incommunication with said frequency dependent amplifier and a firstterminal of a voltage source; and at least one capacitor incommunication with said frequency dependent amplifier and a secondterminal of the voltage source.
 5. The oscillator of claim 3 whereinsaid attenuating device comprises a capacitor.
 6. An oscillator having afundamental frequency and having low phase noise comprising: a frequencydependent amplifier; a frequency dependent feedback device incommunication with an output of said frequency dependent amplifier andan input of said frequency dependent amplifier; and an attenuatingdevice in communication with said frequency dependent amplifier toattenuate noise signals having a frequency much less than thefundamental frequency, wherein said frequency dependent amplifieramplifies an input by a predetermined gain factor, and wherein saidfrequency dependent feedback device comprises: a frequency dependentgain determining impedance in communication with said amplifier, whereina maximum gain of said frequency dependent amplifier occurs at thefundamental frequency; a second attenuating device, and wherein saidfrequency dependent amplifier comprises: a first pair of cross-coupledMOS transistors of a first conductivity type having a drain of each ofsaid first pair of cross-coupled MOS transistors being in communicationwith a gate of the other of said first pair of cross-coupled MOStransistors and to a corresponding terminal of said frequency dependentgain determining impedance; a first current source in communication witha source of one of said first pair of cross-coupled MOS transistors ofthe first conductivity type and with a first terminal of saidattenuating device; a second current source in communication with asource of a second one of said first pair of cross-coupled MOStransistors of the first conductivity type and with a second terminal ofsaid attenuating device; a second pair of cross-coupled MOS transistorsof a second conductivity type whereby a drain of each of said secondpair of cross-coupled MOS transistors is connected to a gate of theother of said second pair of cross-coupled MOS transistors and to oneterminal of said frequency dependent gain determining impedance; a thirdcurrent source in communication with a source of one of said second pairof cross-coupled MOS transistors and with a first terminal of saidsecond attenuating device; and a fourth current source in communicationwith a source of the other of said second pair of cross-coupled MOStransistors of the second conductivity type and with a second terminalof said second attenuating device.
 7. The oscillator of claim 6 whereinsaid attenuating device comprises a first capacitor.
 8. The oscillatorof claim 6 wherein said second attenuating device comprises a secondcapacitor.
 9. An LC oscillator having a fundamental frequency and havinglow phase noise comprising: a frequency dependent amplifier comprising:a pair of cross-coupled MOS transistors of a first conductivity type, adrain of each of said pair of cross-coupled MOS being in communicationwith a gate of the other one of said pair of cross-coupled MOStransistors, a first current source in communication with a source ofone of said pair of cross-coupled MOS transistors, and a second currentsource in communication with a source of another of said pair ofcross-coupled MOS transistors; a frequency dependent gain determiningcircuit comprising: a first inductor in communication with the drain ofsaid one of said pair of cross-coupled MOS transistors and a firstterminal of a voltage source, a second inductor in communication withthe drain of the other of said pair of cross-coupled MOS transistors andthe first terminal of the voltage source, a first capacitor incommunication with the drain of said one of said of said pair ofcross-coupled MOS transistors and a second terminal of the voltagesource, and a second capacitor in communication with the drain of theother of said pair of cross-coupled MOS transistors and the secondterminal of the voltage source; and an attenuating device incommunication with said frequency dependent amplifier to reduce the gainof signals having frequencies less than the fundamental frequency todecrease the phase noise, wherein said attenuating device comprises athird capacitor in communication with said first and second currentsources, wherein said attenuating device has a characteristic such thatthe fundamental frequency is from approximately ten times to twentytimes a high pass bandwidth of a combination of said frequency dependentamplifier and said attenuating device.
 10. An LC oscillator having afundamental frequency and having low phase noise comprising: a frequencydependent amplifier comprising: a pair of cross-coupled MOS transistorsof a first conductivity type, a drain of each of said pair ofcross-coupled MOS being in communication with a gate of the other one ofsaid pair of cross-coupled MOS transistors, a first current source incommunication with a source of one of said pair of cross-coupled MOStransistors, and a second current source in communication with a sourceof another of said pair of cross-coupled MOS transistors; a frequencydependent gain determining circuit comprising a first inductor incommunication with the drain of said one of said pair of cross-coupledMOS transistors and a first terminal of a voltage source, a secondinductor in communication with the drain of the other of said pair ofcross-coupled MOS transistors and the first terminal of the voltagesource, a first capacitor in communication with the drain of said one ofsaid of said pair of cross-coupled MOS transistors and a second terminalof the voltage source, and a second capacitor in communication with thedrain of the other of said pair of cross-coupled MOS transistors and thesecond terminal of the voltage source; and an attenuating circuit incommunication with said frequency dependent amplifier to reduce the gainof signals having frequencies less than the fundamental frequency todecrease the phase noise, wherein said attenuating circuit comprises athird capacitor in communication with said first and second currentsources, wherein said frequency dependent amplifier further comprises: asecond pair of cross-coupled MOS transistors of a second conductivitytype each having a drain connected to a gate of the other of second pairof cross-coupled MOS, a third current source in communication with asource of one of said second pair of cross-coupled MOS transistors, anda fourth current source in communication with a source of the other ofsaid second pair of cross-coupled MOS.
 11. The LC oscillator of claim 10wherein said attenuating circuit further comprises a fourth capacitor incommunication with said third and fourth current sources.
 12. An RFcommunication device comprising: an oscillator having a fundamentalfrequency and having low phase noise comprising: a frequency dependentamplifier; a frequency dependent feedback device in communication withan output of said frequency dependent amplifier and an input of saidfrequency dependent amplifier; and an attenuating device incommunication with said frequency dependent amplifier to attenuate noisesignals having a frequency much less than the fundamental frequency,wherein said attenuating device has a characteristic such that thefundamental frequency is from approximately ten times to twenty times ahigh pass bandwidth of a combination of the frequency dependentamplifier and the attenuating device; wherein the frequency dependentamplifier comprises a second attenuating device.
 13. The RFcommunication device of claim 12 wherein said device comprises an RFreceiver and said oscillator comprises a local oscillator to demodulatea carrier frequency signal received by said RF receiver.
 14. The RFcommunication device of claim 12 wherein said frequency dependentamplifier amplifies an input signal by a predetermined gain factor, andwherein said frequency dependent feedback device comprises: a frequencydependent gain determining impedance in communication with saidfrequency dependent amplifier, wherein a maximum gain of said frequencydependent amplifier occurs at the fundamental frequency.
 15. The RFcommunication device of claim 14 wherein said frequency dependentamplifier comprises: a pair of cross-coupled MOS transistors having adrain of each of said pair of cross-coupled MOS transistors being incommunication with a gate of the other of said pair of cross-coupled MOStransistors and to a corresponding terminal of said frequency dependentgain determining impedance; a first current source having a firstterminal in communication with a source of a first one of said pair ofcross-coupled MOS transistors and with a first terminal of saidattenuating device; and a second current source having a first terminalin communication with a source of a second one of said pair ofcross-coupled MOS transistors and with a second terminal of saidattenuating device.
 16. The RF communication device of claim 14 whereinsaid frequency dependent gain determining impedance comprises: at leastone inductor in communication with said frequency dependent amplifierand a first terminal of a voltage source; and at least one capacitor incommunication with said frequency dependent amplifier and a secondterminal of the voltage source.
 17. The RF communication device of claim15 wherein said attenuating device comprises a capacitor.
 18. The RFcommunication device of claim 15, and wherein said amplifier comprises:a first pair of cross-coupled MOS transistors of a first conductivitytype having a drain of each of said first pair of cross-coupled MOStransistors being in communication with a gate of the other of saidfirst pair of cross-coupled MOS transistors and to a correspondingterminal of said frequency dependent gain determining impedance; a firstcurrent source in communication with a source of one of said first pairof cross-coupled MOS transistors of the first conductivity type and witha first terminal of said attenuating device; a second current source incommunication with a source of a second one of said first pair ofcross-coupled MOS transistors of the first conductivity type and with asecond terminal of said attenuating device; a second pair ofcross-coupled MOS transistors of a second conductivity type wherein adrain of each of said second pair of cross-coupled MOS transistors isconnected to a gate of the other of said second pair of cross-coupledMOS transistors and to one terminal of said frequency dependent gaindetermining impedance; a third current source in communication with asource of one of said second pair of cross-coupled MOS transistors andwith a first terminal of said second attenuating device; and a fourthcurrent source in communication with a source of the other of saidsecond pair of cross-coupled MOS transistors of the second conductivitytype and to a second terminal of said second attenuating device.
 19. TheRF communication device of claim 18 wherein said attenuating devicecomprises a first capacitor.
 20. The RF communication device of claim 18wherein said second attenuating device comprises a second capacitor. 21.A frequency transforming apparatus having low phase noise comprising: afirst oscillator having a first fundamental frequency comprising: afirst frequency dependent amplifier; a first frequency dependentfeedback device in communication with an output of said first frequencydependent amplifier and an input of said first frequency dependentamplifier; and a first attenuating device in communication with saidfirst frequency dependent amplifier to attenuate noise signals having afrequency much less than the first fundamental frequency; a secondoscillator having a second fundamental frequency comprising: a secondfrequency dependent amplifier; a second frequency dependent feedbackdevice in communication with an output of said second frequencydependent amplifier and an input of said second frequency dependentamplifier; and a second attenuating device in communication with saidsecond frequency dependent amplifier to attenuate noise signals having afrequency much less than the second fundamental frequency; and afrequency dependent coupling circuit having a third fundamentalfrequency in communication with an output of the first oscillator and aninput of the second oscillator, said frequency dependent couplingcircuit comprising: a third frequency amplifier, and a third attenuatingdevice in communication with said third frequency dependent amplifier toattenuate noise signals having frequencies much less than the thirdfundamental frequency.
 22. The frequency transforming apparatus of claim21 wherein said first and second attenuating devices each have arespective characteristic such that the first and second fundamentalfrequencies are from approximately ten times to twenty times a high passbandwidth of a respective combination of said first and second frequencydependent amplifiers, said first and second attenuating devices and saidthird frequency dependent amplifier and said third attenuating device.23. The frequency transforming apparatus of claim 21 wherein said first,second and third frequency dependent amplifiers each amplifies an inputby a respective predetermined gain factor, wherein said first frequencydependent feedback device comprises: a first frequency dependent gaindetermining impedance in communication with said first amplifier,wherein a first maximum gain of said first frequency dependent amplifieroccurs at the first fundamental frequency, and wherein said secondfrequency dependent feedback device comprises: a second frequencydependent gain determining impedance in communication with said secondamplifier, wherein a second maximum gain of said second frequencydependent amplifier occurs at the second fundamental frequency.
 24. Thefrequency transforming apparatus of claim 23 wherein said firstfrequency dependent amplifier comprises: a first pair of cross-coupledMOS transistors having a drain of each of said first pair ofcross-coupled MOS transistors being in communication with a gate of theother of said first pair of cross-coupled MOS transistors and to acorresponding terminal of said first frequency dependent gaindetermining impedance; a first current source having a first terminal incommunication with a source of a first one of said first pair ofcross-coupled MOS transistors and with a first terminal of said firstattenuating device; and a second current source having a first terminalin communication with a source of a second one of said first pair ofcross-coupled MOS transistors and with a second terminal of said firstattenuating device, and wherein said second frequency dependentamplifier comprises: a second pair of cross-coupled MOS transistorshaving a drain of each of said second pair of cross-coupled MOStransistors being in communication with a gate of the other of saidsecond pair of cross-coupled MOS transistors and to a correspondingterminal of said second frequency dependent gain determining impedance;a third current source having a first terminal in communication with asource of a first one of said second pair of cross-coupled MOStransistors and with a first terminal of said second attenuating device;and a fourth current source having a first terminal in communicationwith a source of a second one of said second pair of cross-coupled MOStransistors and with a second terminal of said second attenuatingdevice.
 25. The frequency transforming apparatus of claim 23 whereineach of said first and second frequency dependent gain determiningimpedance comprises: at least one inductor in communication with arespective one of said first and second frequency dependent amplifiersand a first terminal of a voltage source; and at least one capacitor incommunication with said a respective one of said first and secondfrequency dependent amplifiers and a second terminal of the voltagesource.
 26. The frequency transforming apparatus of claim 25 wherein thefirst, second and third attenuating devices each comprises a capacitor.27. The frequency transforming apparatus of claim 23 wherein said firstand second oscillators each comprise another attenuating device, whereinsaid first and second frequency dependent amplifiers each comprises: afirst pair of cross-coupled MOS transistors of a first conductivity typehaving a drain of each of said first pair of cross-coupled MOStransistors being in communication with a gate of the other of saidfirst pair of cross-coupled MOS transistors and to a correspondingterminal of a respective one of said frequency dependent gaindetermining impedances; a first current source in communication with asource of one of said first pair of cross-coupled MOS transistors of thefirst conductivity type and with a first terminal of a respective one ofsaid attenuating devices; a second current source in communication witha source of a second one of said first pair of cross-coupled MOStransistors of the first conductivity type and with a second terminal ofa respective one of said attenuating devices; a second pair ofcross-coupled MOS transistors of a second conductivity type wherein adrain of each of said second pair of cross-coupled MOS transistors isconnected to a gate of the other of said second pair of cross-coupledMOS transistors and to one terminal of a respective one of saidfrequency dependent gain determining impedances; a third current sourcein communication with a source of one of said second pair ofcross-coupled MOS transistors and with a first terminal of a respectiveone of said other attenuating devices; and a fourth current source incommunication with a source of the other of said second pair ofcross-coupled MOS transistors of the second conductivity type and to afourth second terminal of a respective one of said other attenuatingdevices.
 28. The frequency transforming apparatus of claim 27 whereinsaid first attenuating device and said respective other attenuatingdevice each comprises a first capacitor.
 29. The frequency transformingapparatus of claim 28 wherein said second attenuating device and saidrespective other attenuating device each comprises a second capacitor.30. The frequency transforming apparatus of claim 21 wherein saidfrequency dependent coupling circuit is selected from the group ofcoupling circuits consisting of phase shifters, frequency mixers,frequency shifters, modulators, and demodulators.
 31. A multiplefrequency oscillation circuit having low phase noise, comprising: afirst oscillator having a first fundamental frequency comprising: afirst frequency dependent amplifier; a first frequency dependentfeedback device in communication with an output of said first frequencydependent amplifier and an input of said first frequency dependentamplifier; and a first attenuating device in communication with saidfirst frequency dependent amplifier to attenuate noise signals having afrequency much less than the first fundamental frequency; a secondoscillator having a second fundamental frequency comprising: a secondfrequency dependent amplifier; a second frequency dependent feedbackdevice in communication with an output of said second frequencydependent amplifier and an input of said second frequency dependentamplifier; and a second attenuating device in communication with saidsecond frequency dependent amplifier to attenuate noise signals having afrequency much less than the second fundamental frequency; and afrequency dependent coupling circuit having a third fundamentalfrequency in communication with an output of the first oscillator and aninput of the second oscillator, said frequency dependent couplingcircuit comprising: a third frequency dependent amplifier, and a thirdattenuating device in communication with said third frequency dependentamplifier to attenuate noise signals having frequencies much less thanthe third fundamental frequency.
 32. The multiple frequency oscillationcircuit of claim 31 wherein said first and second attenuating deviceseach has a respective characteristic such that the first and secondfundamental frequencies are from approximately ten times to twenty timesa high pass bandwidth of a respective combination of said first andsecond frequency dependent amplifiers, said first and second attenuatingdevices and said third frequency dependent amplifier and said thirdattenuating device.
 33. The multiple frequency oscillation circuit ofclaim 31 wherein said first, second and third frequency dependentamplifiers each amplifies an input by a respective predetermined gainfactor, wherein said first frequency dependent feedback devicecomprises: a first frequency dependent gain determining impedance incommunication with said first frequency dependent amplifier, wherein afirst maximum gain of said first frequency dependent amplifier occurs atthe first fundamental frequency, and wherein said second frequencydependent feedback device comprises: a second frequency dependent gaindetermining impedance in communication with said second frequencydependent amplifier, wherein a second maximum gain of said secondfrequency dependent amplifier occurs at the second fundamentalfrequency.
 34. The multiple frequency oscillation circuit of claim 33wherein said first frequency dependent amplifier comprises: a first pairof cross-coupled MOS transistors having a drain of each of said firstpair of cross-coupled MOS transistors being in communication with a gateof the other of said first pair of cross-coupled MOS transistors and toa corresponding terminal of said first frequency dependent gaindetermining impedance; a first current source having a first terminal incommunication with a source of a first one of said first pair ofcross-coupled MOS transistors and with a first terminal of said firstattenuating device; and a second current source having a first terminalin communication with a source of a second one of said first pair ofcross-coupled MOS transistors and with a second terminal of said firstattenuating device, and wherein said second frequency dependentamplifier comprises: a second pair of cross-coupled MOS transistorshaving a drain of each of said second pair of cross-coupled MOStransistors being in communication with a gate of the other of saidsecond pair of cross-coupled MOS transistors and to a correspondingterminal of said second frequency dependent gain determining impedance;a third current source having a first terminal in communication with asource of a first one of said second pair of cross-coupled MOStransistors and with a first terminal of said second attenuating device;and a fourth current source having a first terminal in communicationwith a source of a second one of said second pair of cross-coupled MOStransistors and with a second terminal of said second attenuatingdevice.
 35. The multiple frequency oscillation circuit of claim 33wherein each of said first and second frequency dependent gaindetermining impedances comprises: at least one inductor in communicationwith a respective one of said first and second frequency dependentamplifiers and a first terminal of a voltage source; and at least onecapacitor in communication with said respective one of said first andsecond amplifiers and a second terminal of the voltage source.
 36. Themultiple frequency oscillation circuit of claim 35 wherein said first,second and third attenuating devices each comprises a capacitor.
 37. Themultiple frequency oscillation circuit of claim 33 wherein said firstand second oscillators each comprises another attenuating device,wherein said first and second frequency dependent amplifiers eachcomprises: a first pair of cross-coupled MOS transistors of a firstconductivity type having a drain of each of said first pair ofcross-coupled MOS transistors being in communication with a gate of theother of said first pair of cross-coupled MOS transistors and to acorresponding terminal of a respective one of said frequency dependentgain determining impedances; a first current source in communicationwith a source of one of said first pair of cross-coupled MOS transistorsof the first conductivity type and with a first terminal of a respectiveone of said attenuating devices; a second current source incommunication with a source of a second one of said first pair ofcross-coupled MOS transistors of the first conductivity type and with asecond terminal of a respective one of said attenuating devices; asecond pair of cross-coupled MOS transistors of a second conductivitytype whereby a drain of each of said second pair of cross-coupled MOStransistors is connected to a gate of the other of said second pair ofcross-coupled MOS transistors and to one terminal of a respective one ofsaid frequency dependent gain determining impedances; a third currentsource in communication with a source of one of said second pair ofcross-coupled MOS transistors and with a first terminal of a respectiveone of said other attenuating devices; and a fourth current source incommunication with a source of the other of said second pair ofcross-coupled MOS transistors of the second conductivity type and to afourth second terminal of a respective one of said other attenuatingdevices.
 38. The multiple frequency oscillation circuit of claim 37wherein said first attenuating device and said respective otherattenuating device each comprises a first capacitor.
 39. The multiplefrequency oscillation circuit of claim 38 wherein said secondattenuating device and said respective other attenuating device eachcomprises a second capacitor.
 40. The multiple frequency oscillationcircuit of claim 31 wherein said frequency dependent coupling circuitgenerate phase shifts of the first and second fundamental frequencies.41. The multiple frequency oscillation circuit of claim 40 wherein thefirst and second fundamental frequencies are 90° out of phase.
 42. Aquadrature oscillator circuit having low phase noise, comprising: afirst oscillator having a first fundamental frequency comprising: afirst frequency amplifier; a first frequency dependent feedback devicein communication with an output of said first frequency dependentamplifier and an input of said first frequency dependent amplifier tofeed a portion of an amplified signal having the first fundamentalfrequency to an input of said first frequency dependent amplifier; and afirst attenuating device in communication with said first frequencydependent gain amplifier for reducing the gain of said first frequencydependent amplifier for signals having frequencies much less than thefirst fundamental frequency to decrease said phase noise; and a firstfrequency dependent coupling circuit having a second fundamentalfrequency having an input in communication with the output of the firstfrequency dependent amplifier, said first frequency dependent couplingcircuit comprising: a second frequency dependent amplifier, and a secondattenuating device in communication with said second frequency dependentamplifier for reducing the gain of said frequency dependent amplifierfor signals having frequencies much less than said second fundamentalfrequency to decrease said phase noise; a second oscillator to generatea second fundamental signal having a third fundamental frequency havinglow phase noise, in communication with an output of the second frequencydependent amplifier, and said second oscillator comprising: a thirdfrequency dependent amplifier; a respective frequency dependent feedbackdevice in communication with an output of said third frequency dependentamplifier and an input of said third frequency dependent amplifier tofeed a portion of an amplified signal having the third fundamentalfrequency to an input of said third frequency dependent amplifier; and athird attenuating device in communication with the third frequencydependent amplifier for reducing the gain of said third frequencydependent amplifier for signals having frequencies much less than thethird fundamental frequency to decrease the phase noise; and a secondfrequency dependent coupling circuit having a fourth fundamentalfrequency having an input in communication with the output of said thirdfrequency dependent amplifier and the input of said first frequencydependent such that a phase of the third fundamental frequency isreversed relative to a phase of the first fundamental frequency, andcomprising: a fourth frequency dependent amplifier, and a fourthattenuating device in communication with said second frequency dependentamplifier for reducing the gain of said fourth frequency dependentamplifier for signals having frequencies much less than said fourthfundamental frequency to decrease the phase noise.
 43. The quadratureoscillator circuit of claim 42 wherein said first, second, third andfourth attenuating devices each has a characteristic such that thefirst, second, third and fourth fundamental frequencies are each fromapproximately ten times to twenty times a high pass bandwidth of arespective combination of said first frequency dependent amplifier andsaid first attenuating device and of said third frequency dependentamplifier and said third attenuating device.
 44. The quadratureoscillator circuit of claim 42 wherein said first, second, third andfourth frequency dependent amplifiers each amplify an input signal byrespective predetermined gain factors, wherein said first, second, thirdand fourth frequency dependent each comprises: a frequency dependentgain determining impedance in communication with a corresponding one ofsaid first, second, third and fourth frequency dependent amplifiers,wherein the maximum gain of each of said corresponding one of saidfirst, second, third and fourth frequency dependent amplifiers, occursat a respective one of the first, second, third and fourth fundamentalfrequencies.
 45. The quadrature oscillator circuit of claim 44 whereineach of said first, second, third and fourth frequency dependentamplifiers comprises: a pair of cross-coupled MOS transistors whereby adrain of each of pair of cross-coupled MOS transistors is incommunication with a gate of another one of said pair of cross-coupledMOS transistors and said frequency dependent gain determining impedance;a first current source in communication with a source of one of saidpair of cross-coupled MOS transistors and to a first terminal of avoltage source and to a first terminal of a respective one of saidfirst, second, third and fourth attenuating devices; and a secondcurrent source in communication with a source of the other one of saidpair of cross-coupled MOS transistors and to a first terminal of arespective one of said first, second, third and fourth attenuatingdevices.
 46. The quadrature oscillator circuit of claim 44 wherein eachof said first, second, third and fourth frequency dependent gaindetermining impedances comprises: at least one inductor in communicationwith of a respective one of said first, second, third and fourthamplifiers and a second terminal of the voltage source; and at least onecapacitor in communication with of a respective one of said first,second, third and fourth amplifiers and a third terminal of the voltagesource.
 47. The quadrature oscillator circuit of claim 46 wherein eachof said first, second, third and fourth attenuating devices comprises acapacitor.
 48. The quadrature oscillator circuit of claim 44 whereineach of said first, second, third and fourth frequency dependentamplifiers comprises: an additional attenuating device; a firstcross-coupled pair of MOS transistors of the first conductivity typehaving a drain of each of said first cross-coupled pair of MOStransistors in communication with a gate of the other of said firstcross-coupled pair of MOS transistors and to a terminal of a respectiveone of said first, second, third and fourth frequency dependent gaindetermining impedances; a first current source in communication with asource of one of said first-coupled pair of MOS transistors and to afirst terminal of a respective one of said first, second, third andfourth attenuating devices; a second current source in communicationwith a source of the other said first cross-coupled pair of MOStransistors and to a terminal of a respective one of said first, second,third and fourth attenuating devices; a second cross-coupled pair of MOStransistors of the second conductivity type have a drain of each ofsecond cross-coupled pair of MOS transistors in communication with agate of the other of second cross-coupled pair of MOS transistors and tothe first terminal of a respective one of said first, second, third andfourth attenuating devices; a third current source in communication witha source of one of said second cross-coupled pair of MOS transistors andto a first terminal of said additional attenuating device; and a fourthcurrent source in communication with a source of the other of saidsecond cross-coupled pair of MOS transistors and to a second terminal ofsaid additional attenuating device.
 49. The quadrature oscillatorcircuit of claim 48 wherein said first, second, third and fourthattenuating devices each comprises a first capacitor.
 50. The quadratureoscillator circuit of claim 48 said additional attenuating devicecomprises a second capacitor.
 51. The quadrature oscillator circuit ofclaim 40 wherein said second frequency dependent coupling circuitgenerates a phase shift of the second fundamental frequency.
 52. Adifferential amplifier possessing low phase noise, comprising: a firsttransistor having a first terminal to receive an in-phase signal, and asecond terminal to provide an out-of-phase signal; a second transistorhaving a first terminal to receive the out-of-phase signal, and a secondterminal to provide the in-phase signal; a first biasing source incommunication with a third terminal of said first transistor and a firstterminal of a voltage source; a second biasing source in communicationwith a third terminal of the second transistor and the first terminal ofthe voltage source; and an attenuating capacitor in communication withthe third terminal of said first transistor and the third terminal ofsaid second transistor, said capacitor decreases gain of saiddifferential amplifier at low frequencies to eliminate phase noisecomponents from the in-phase and the out-of-phase signals, wherein ahigh pass bandwidth of said differential amplifier is determined asfollows: ${BW} = \frac{g_{m}}{2\pi \quad {Cc}}$

where: BW is the high pass bandwidth, g_(m) is the transconductance ofsaid first and second transistors as measured as the third terminals,and Cc is the value of said attenuating capacitor, wherein the high passbandwidth is less than a cutoff frequency of a circuit employing saiddifferential amplifier, and wherein the differential amplifier comprisesanother attenuating capacitor.
 53. The differential amplifier of claim52 wherein the cutoff frequency of the circuit containing saiddifferential amplifier is from approximately 10 times to approximately20 times the high pass bandwidth of said differential amplifier.
 54. Thedifferential amplifier of claim 52 wherein said first and secondtransistors are selected from the group of transistors consisting ofNMOS transistors, PMOS transistors, and bipolar transistors.
 55. Thedifferential amplifier of claim 52 wherein said first and second biasingsources are selected from the group of biasing sources consisting ofcurrent sources and resistors.
 56. An LC oscillator having a fundamentalfrequency and having low phase noise comprising: a frequency dependentamplifier comprising: a pair of cross-coupled MOS transistors of a firstconductivity type, a drain of each of said pair of cross-coupled MOSbeing in communication with a gate of the other one of said pair ofcross-coupled MOS transistors, a first current in communication with asource of one of said pair of cross-coupled MOS transistors, whereinsaid first current source comprises a first programmable resistance, anda second current source in communication with a source of another ofsaid pair of cross-coupled MOS transistors, wherein said second currentsource comprises a second programmable resistance; a capacitance incommunication with the source of the one of said pair of cross-coupledMOS transistors and the source of another of said pair of cross-coupledMOS transistors to filter flicker noise; a frequency dependent gaindetermining circuit comprising a first inductor in communication withthe drain of said one of said pair of cross-coupled MOS transistors anda first terminal of a voltage source, a second inductor in communicationwith the drain of the other of said pair of cross-coupled MOStransistors and the first terminal of the voltage source, a firstcapacitor in communication with the drain of said one of said of saidpair of cross-coupled MOS transistors and a second terminal of thevoltage source, and a second capacitor in communication with the drainof the other of said pair of cross-coupled MOS transistors and thesecond terminal of the voltage source.
 57. An LC oscillator having afundamental frequency and having low phase noise comprising: a frequencydependent amplifier comprising: a pair of cross-coupled MOS transistorsof a first conductivity type, a drain of each of said pair ofcross-coupled MOS being in communication with a gate of the other one ofsaid pair of cross-coupled MOS transistors, a first current source incommunication with a source of one of said pair of cross-coupled MOStransistors, wherein said first current source comprises a firstprogrammable resistance, and a second current source in communicationwith a source of another of said pair of cross-coupled MOS transistors,wherein said second current source comprises a second programmableresistance; a frequency dependent gain determining circuit comprising afirst inductor in communication with the drain of said one of said pairof cross-coupled MOS transistors and a first terminal of a voltagesource, a second inductor in communication with the drain of the otherof said pair of cross-coupled MOS transistors and the first terminal ofthe voltage source, a first capacitor in communication with the drain ofsaid one of said of said pair of cross-coupled MOS transistors and asecond terminal of the voltage source, and a second capacitor incommunication with the drain of the other of said pair of cross-coupledMOS transistors and the second terminal of the voltage source, whereinthe first current source comprises the first inductor in communicationwith said first programmable resistance, and wherein the second currentsource comprises the second inductor in communication with said secondprogrammable resistance.
 58. An LC oscillator having a fundamentalfrequency and having low phase noise comprising: a frequency dependentamplifier comprising: a pair of cross-coupled MOS transistors of a firstconductivity type, a drain of each of said pair of cross-coupled MOSbeing in communication with a gate of the other one of said pair ofcross-coupled MOS transistors, a first current source in communicationwith a source of one of said pair of cross-coupled MOS transistors,wherein said first current source comprises a first programmableinductance, and a second current source in communication with a sourceof another of said pair of cross-coupled MOS transistors, wherein saidsecond current source comprises a second programmable inductance; acapacitance in communication with the source of the one of said pair ofcross-coupled MOS transistors and the source of another of said pair ofcross-coupled MOS transistors to filter flicker noise; a frequencydependent gain determining circuit comprising: a first inductor incommunication with the drain of said one of said pair of cross-coupledMOS transistors and a first terminal of a voltage source, a secondinductor in communication with the drain of the other of said pair ofcross-coupled MOS transistors and the first terminal of the voltagesource, a first capacitor in communication with the drain of said one ofsaid of said pair of cross-coupled MOS transistors and a second terminalof the voltage source, and a second capacitor in communication with thedrain of the other of said pair of cross-coupled MOS transistors and thesecond terminal of the voltage source.
 59. An LC oscillator having afundamental frequency and having low phase noise comprising: a frequencydependent amplifier comprising: a pair of cross-coupled MOS transistorsof a first conductivity type, a drain of each of said pair ofcross-coupled MOS being in communication with a gate of the other one ofsaid pair of cross-coupled MOS transistors, a first current source incommunication with a source of one of said pair of cross-coupled MOStransistors, and a second current source in communication with a sourceof another of said pair of cross-coupled MOS transistors; a frequencydependent gain determining circuit comprising a first inductor incommunication with the drain of said one of said pair of cross-coupledMOS transistors and a first terminal of a voltage source, a secondinductor in communication with the drain of the other of said pair ofcross-coupled MOS transistors and the first terminal of the voltagesource, a first capacitor in communication with the drain of said one ofsaid of said pair of cross-coupled MOS transistors and a second terminalof the voltage source, and a second capacitor in communication with thedrain of the other of said pair of cross-coupled MOS transistors and thesecond terminal of the voltage source; and an attenuating circuit incommunication with said frequency dependent amplifier to reduce the gainof signals having frequencies less than the fundamental frequency todecrease the phase noise, wherein said attenuating circuit comprises athird capacitor in communication with said first and second currentsources, wherein said first current source comprises a firstprogrammable resistance, and wherein said second current sourcecomprises a second programmable resistance.
 60. An LC oscillator havinga fundamental frequency and having low phase noise comprising: afrequency dependent amplifier comprising: a pair of cross-coupled MOStransistors of a first conductivity type, a drain of each of said pairof cross-coupled MOS being in communication with a gate of the other oneof said pair of cross-coupled MOS transistors, a first current source incommunication with a source of one of said pair of cross-coupled MOStransistors, and a second current source in communication with a sourceof another of said pair of cross-coupled MOS transistors; a frequencydependent gain determining circuit comprising a first inductor incommunication with the drain of said one of said pair of cross-coupledMOS transistors and a first terminal of a voltage source, a secondinductor in communication with the drain of the other of said pair ofcross-coupled MOS transistors and the first terminal of the voltagesource, a first capacitor in communication with the drain of said one ofsaid of said pair of cross-coupled MOS transistors and a second terminalof the voltage source, and a second capacitor in communication with thedrain of the other of said pair of cross-coupled MOS transistors and thesecond terminal of the voltage source; and an attenuating circuit incommunication with said frequency dependent amplifier to reduce flickernoise, wherein said attenuating circuit comprises a third capacitor incommunication with said first and second current sources, wherein saidfirst current source comprises a first programmable inductance, andwherein said second current source comprises a second programmableinductance.